Prompt, definitive detection and timing of the onset of myocardial infarction as well as prompt detection of reperfusion are essential to optimize therapy and evaluate the effects of thrombolytic agents. However, conventional methods including detection of changes in activity of total creatine kinase (CK) or its isoenzymes in plasma are neither rapid nor sufficiently sensitive to permit reliable, early diagnosis. Recent discovery that MM isoenzyme of CK released by myocardium after infarction (MMA) undergoes modification in plasma to yield two additional enzymatically active isoforms (MMB and MMC) that are separated by cromatofocusing may provide an alternative set of criteria. Because of continuous conversion of MMA to MMB and MMC, normal plasma contains relatively little MMA. Thus, early egress of a modest amount of MMA from myocardium alters isoform profiles in plasma markedly and promptly after the onset of tissue injury. Utilization of changes in isoform profiles for early detection and precise timing of the onset of infarction and reperfusion requires characterization of kinetic parameters and the pathophysiology of infarction affecting the time-course of isoform profiles in plasma in vivo. Accordingly, factor(s) responsible for isoform conversion will be identified by selective immunoprecipitation of individual peptidases from canine plasma in vitro and quantitative assays for each developed. Separate intravenous injections of purified isoforms in conscious dogs with and without concomitant inhibition of plasma isoform converting factor(s) by infusion of selective inhibitors will be used to determine the rates of clearance and conversion of isoforms in vivo. These rates and the extent of isoform conversion in cardiac lymph evaluated after coronary artery occlusion with and without recanalization will permit development of a physiologic model of isoform kinetics in vivo. Serial isoform profiles in plasma in conscious dogs after persistent coronary occlusion or recanalization will be analyzed using the model to define specific criteria for detection and timing of the onset of myocardial infarction and reperfusion. Experiments in other dogs will determine whether factors typical of human infarction such as recanalization into residual stenosis affect isoform profiles and the criteria for their evaluation. The proposed studies in dogs will acquire the information needed ultimately for application of MM CK isoform analysis as a method to rapidly and reliably detect infarction and reperfusion in man.